Wells are drilled on land and in marine environments for a variety of exploratory and extractive purposes. Due to the variety of purposes, the conditions experienced while producing the wells also vary greatly. The particular conditions include changes in temperature, pressure, subterranean fluids and formations, among other variables. The conditions expected during the drilling process affect the type of drilling process used to produce the wellbore. The type of drilling operation will vary with changes in the conditions. The equipment used, including the configuration of the bottomhole assembly, will also be affected by subsurface conditions.
A drilling system includes a drilling rig outside of the wellbore and a drill string with a bottomhole assembly near or at the bottom of the wellbore. The drilling rig includes a platform, a rotating table, a kelly, pressure control devices such as one or more blowout preventers and a rotating control device (“RCD”). The drilling rig stabilizes and controls the upper end of the drill string, which extends downward. The drill string includes drill pipe in segments mated together at threaded joints. The drill pipe provides force transmission and a fluid conduit down to the bottomhole assembly at the end of the drill pipe. The bottom of the drill pipe is connected to the bottomhole assembly. The bottomhole assembly has a variety of equipment and modules that enable operators to monitor and control the drilling progress. The bottomhole assembly includes components such as a drill bit, a drill motor, measurement-while-drilling equipment, logging-while-drilling equipment, and a drill collar.
During drilling, a drilling fluid is pumped from the drilling rig down the fluid conduit within the drill pipe to the bottomhole assembly. The drilling fluid passed through a fluid conduit extending through the bottomhole assembly and passes through the drill bit, producing a positive pressure at the bottom of the wellbore. The composition of the drilling fluid also changes depending on the conditions of the formation through which the wellbore will extend. Generally, however, the drilling fluid is used to lubricate and cool the drill bit while also removing drill cuttings from the wellbore. The drilling fluid flows back up the wellbore in annular gap around the drill string, carrying drill cuttings with it.
As the drilling fluid reaches the top of the drilling system, the rotating control device creates a closed circulatory path for the drilling fluid pumped into the wellbore. The RCD provides a rotatable seal between the drill string and the encasing structure, which acts as an outlet to divert the drilling fluid through a series of separators and treatment devices before being pumped back down into the wellbore to circulate through again. The RCD includes a fluid seal that contains the pressurized drilling fluid while also allowing rotation of the drill string. Bearings contained in the RCD allow rotation of part of the RCD and affect the thickness of the device structure.